1. Field of the Invention
The present invention relates to a discharge amount measuring device and method for a rotational electric machine.
2. Description of Related Art
A rotational electric machine such as an electric motor or generator includes a coil, and the coil may directly contact with a casing or core of the rotational electric machine. When the machine includes plural coils, the coils may directly contact with each other. The coil is insulated by an insulating film. However, discharge may be generated by applying a pulse voltage. If discharge is generated, the insulating film is damaged. Further, a short may be generated, if the insulating film is completely damaged. Therefore, a discharge amount or insulating performance is required to be measured.
JP-A-2006-098170 discloses a method of measuring a discharge amount. A current waveform is detected by a high frequency current transformer, and the detected waveform is filtered by a high-pass filter. Thus, only discharge pulse is extracted, and a discharge amount is calculated based on a peak value of the extracted pulse.
JP-A-2005-274440 discloses a method of measuring a discharge amount. A current waveform is detected by a current sensor, and an electromagnetic waveform is detected by an electromagnetic sensor. Fourier transform is performed relative to the current waveform and the electromagnetic waveform. A discharge amount is calculated based on a variation of a high frequency component of the Fourier transform.
JP-A-2006-038688 discloses a method of measuring a discharge amount. A discharge amount is calculated by measuring a partial discharge current, when a surge voltage is intentionally applied to a coil of a motor with a predetermined frequency 50 Hz-20 kHz by using a surge voltage generating device.
However, a frequency of a discharge pulse generated in the motor is high. Further, an impedance of the coil of the motor is complicated, because the impedance is represented by a distribution constant. Therefore, a discharge generated in the motor is easily diffused, and an amount of current flowing through a sensor may not correspond to an actual amount of the discharge. That is, the current passing through the sensor is only a part of the actual discharge amount. Thus, the discharge amount measured by using the above method is smaller than the actual discharge amount.